A team of University of Queensland researchers asked 771 construction workers to report their sense of job satisfaction and emotional exhaustion.

"Consistent with previous research," the BPS Research Digest summarizes, "well-being was correlated with age, with job satisfaction dropping in the late 20s and recovering in the early 40s, and emotional exhaustion showing the reverse pattern."

The researchers dug in and found the reasons why:

• Support from coworkers drops in your 30s. Everyone is trying to shoulder their way through "promotion bottlenecks," so they're less likely to help you. But when you're in your 20s, people want to make friends.

• Time pressure increases. When you hit your 30s, the expectations for success goes up — so you throw more of yourself into work, which can be emotionally exhausting.

The findings are robust, since the research shows that participants' happiness at work fell in their 30s regardless of gender, education levels, and whether they had blue- or white-collar jobs.

But the study isn't perfect. It focuses on the construction industry, and the sample was mostly men, which hampers the data in a number of ways, like with the emotional fatigue related to raising a family.